The goal of this project is to determine the molecular mechanism by which two abused drugs, nicotine and cocaine, interact with neuronal nicotinic acetyicholine receptors (nAChRs) in the peripheral and central nervous systems. Cocaine exerts its euphoric, addictive nature through the dopamine transport system, but some of its toxic effects are mediated by subtypes of neuronal nAChRs. nAChRs regulate signal transmission between many central nervous system neurons and at the neuromuscular junction, and both nicotine and cocaine affect their function. Reports in the literature have suggested that cocaine and other local anesthetics, when administered intraventricularly, are antagonistic to the behavioral and pharmacological effects of nicotine. We have identified RNA sequences (RNA aptamers) that interact with nAChRs and can alleviate the effects of cocaine without affecting receptor function. Likewise, several cocaine derivatives have been identified with similar properties. One aim of this proposal is to extend these studies to a variety of neuronal nAChR subtypes in order to develop specific agents that will alleviate the effects of cocaine and the inhibitory effects of (-)nicotine. The second group of studies will build on our previous work indicating that the effects of cocaine are mediated by at least two sites which differ among neuronal nAChR subtypes. Stably transfected cell lines and a newly developed transfection system will be used to study the transient kinetics of various subtypes of neuronal nAChRs in order to characterize in more detail the binding sites for cocaine and nicotine. Rapid mixing techniques and laser-pulse photolysis will be used to provide temporal resolution on the muS to ms timescale. The molecular mechanism, including knowledge of the concentration at which nicotine and cocaine affect specific nAChRs, will provide a basis for mechanism-based design of therapeutic agents that alleviate some effects of the drugs without themselves having deleterious effects. The knowledge gained is expected to contribute to the rational treatment of the millions of individuals adversely affected by cocaine and nicotine.